When I bought a new bike last year I specified claipers because I didnt want the weight penalty when going up hills (and the extra cost. Its not only the weight of the brake units, but the wheels and forks are also heavier. The rear disk can provide problems with attaching a rack. Since the rear brake is only a back-up system you could consider a front disk only. Recent calipers with pads mounted with spherical washers and nuts are much easier to adjust than the ones from 12 yrs ago with the post mounted pads. Kool stop pads will give all the wet weather braking you need. Disks make sense if you will ride a MTB through mud or a loaded tourer on long descents.